Dam Safety & Security

FERC proposes expanding PFMA process to more dams

The Federal Energy Regulatory Commission (FERC) proposes applying the Potential Failure Mode Analyses (PFMA) process to more dams. The process would be expanded to include significant-hazard-potential dams that do not require Part 12D inspections. Additionally, low-hazard-potential dams greater than 9 feet tall or which impound more than 25 acre-feet would be included.

Part 12D inspections are inspections performed by an independent consultant, as stipulated in Part 12 of the commission’s regulations for the safety of hydropower projects and project works.

PFMAs are conducted by reviewing available information about a dam and then analyzing the ways in which the dam could potentially fail, through a facilitated discussion among representatives of the owner, including the consultant, if applicable, and a FERC inspector.

Over the past six years, FERC has conducted PFMAs for all high- and significant-hazard-potential dams that require Part 12D inspections.

FERC said it would refine the proposed process as necessary, based on completion of several regional pilot projects and feedback from dam owners. It anticipates implementing the program before the end of 2008. FERC envisions it could take up to six years to complete all new analyses.

In a letter to dam owners, FERC said it anticipates the scope of PFMAs for the low-hazard-potential dams will be less involved and less complex than PFMAs for projects subject to Part 12D inspections.

For significant-hazard-potential dams that do not require Part 12D inspections and for low-hazard-potential dams, the PFMA would be accomplished as part of the FERC dam safety inspection.

FERC said the PFMA process, part of the commission’s Dam Safety Performance Monitoring Program, has been highly successful in providing an improved understanding by all parties of the design and construction, history, and operation of the project. It also has improved understanding of how each of the aspects influences potential failure modes of a particular structure.

Significant-hazard-potential dams

For significant-hazard-potential dams without a Part 12D inspection, the owner would take the lead in the PFMA, under FERC’s proposal. The owner is to follow guidance provided in Chapter 14 of FERC’s Engineering Guidelines for the Evaluation of Hydropower Projects.

The owner can perform the program with in-house dam safety knowledge, experience, and expertise, if available, or by retaining a consultant, FERC said. The facilitator should be a civil engineer with a broad background and experience in dam safety. A FERC engineer is to participate in the PFMA.

Low-hazard potential dams

For low-hazard-potential dams greater than 9 feet tall, or that impound more than 25 acre-feet, the proposal calls for the FERC project engineer normally to serve as the facilitator, and to lead the PFMA and the inspection.

However, FERC said, dam owners who prefer to take the lead and conduct the PFMA will be encouraged to do so.

Michigan utility begins rebuilding Silver Lake Dam

Upper Peninsula Power Co. is rebuilding the failed Silver Lake Dam, part of the 11.2-MW Dead River hydroelectric project in Michigan.

The dam was breached by an emergency fuse plug failure in May 2003. (See "Dam Safety & Security," September 2007.)

UPPCO said is building a new 150-foot-long concrete spillway, lengthening and raising existing dikes, and building a new 450-foot-wide, 40-foot-tall earthen dam at the site of the breach. The company approved up to $17.6 million for the project, of which it already has spent $4.5 million to meet costs for development and design work.

Bacco Construction is providing earthmoving services and subcontracted the concrete work to CR Meyer. STS Consultants is performing quality control and inspection during construction.

The new dam is expected to be in place in 2009.

BC Hydro prepares to strengthen Strathcona Dam

BC Hydro proposes making seismic improvements at its 68-MW Strathcona Dam project, which features the largest earthfill dam on British Columbia’s Vancouver Island.

The 53-meter-tall, 511-meter-long dam impounds the Upper Campbell Reservoir. Two turbine-generating units at the toe of the dam possess a total installed capacity of 68 MW, or enough power to supply 67,000 homes.

Seismic improvements to the dam, constructed in 1958, are to include:

– Adding a downstream rockfill berm to improve dam stability during and after an earthquake;

– Installing new anchors and seismic isolators to the existing concrete intake tower structure to allow it to perform safely in a major earthquake and allow for post-earthquake closure of the intake gates; and

– Anchoring the concrete spillway pier to prevent possible separation from the dam during an earthquake.

Although the project is in the preliminary design stage, BC Hydro has estimated it could cost as much as C$70 million (US$69.4 million) to mitigate piping and seismic risk at the dam. (See "Dam Safety & Security," October 2007.)

The tendering process is not expected to start before summer 2009, with work beginning in later 2009 or early 2010.

Dam safety upgrade work is expected to take three to four years to complete.

For an eight- to 12-month period during intake tower work, there will be no water flow through the generating station, and therefore no power generation.